Heat energized refrigerator



Jan. 10, 1967 M. J. MALIK HEAT ENERGIZED REFRIGERATOR 2 Sheets-Sheet 1 Filed Aug. 25, 1965 ATTORNEY Jan. 10, 1967 M. J. MALIK HEAT ENERGIZED REFRIGERATOR Filed Aug. 25, 1965 3 Sheets-Sheet 2 I N VEN TO R.

ATT0RNEY WM W United States Patent 3,296,808 HEAT ENERGEZED REFRIGERATOR Marvin .l. Maliir, Indianapolis, Ind, assiguor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Aug. 25, 1965, Ser. No. 482,531 8 Claims. ((11. 626) My invention relates generally to a heat energized refrigerator and more specifically, to a heat energized refrigerator comprising three variable volume chambers swept by two displacers.

It is generally old to absorb heat from a cold surface to-refrigerate and transfer this absorbed heat to a heat sink without an intermediate transfer of mechanical energy. A practical means of achieving this is the utilization of three variable volume chambers swept by a pair of displacers to transfer a fixed volume of gas between the chambers through regenerative heat exchangers. Such a system is shown and described in the United States patent to Vuilleumier 1,275,507. In such a system, the instantaneous pressure is constant throughout the system at any given time so that theoretically no work is required to move the displacers. However, because of frictional flow losses and pressure drops through the regenerative heat exchangers, a source of mechanical work is required to produce the displacer motion. My invention is directed toward providing this source of mechanical work from the system itself so that no external power source is required and the system can thus be self-sustaining. In general, the object of my invention then is to provide a heat energized refrigerator comprising three variable volume chambers swept by two displacers in which the motion of the displacers is self-sustaining, that is, no external power source is required to drive the displacers.

Another object of my invention is to provide a heat energized refrigerator comprising three variable volume chambers swept by two displacers in which the motion of the displacers is self-sustained through utilization of the pressure fluctuation of the system. Another object of my invention is to provide a heat energized refrigerator comprising three variable volume chambers swept by two displacers in which the motion of the displacers is self-sustained by incorporating the displacers in a spring-mass system vibrating at resonance frequency,

Another object of my invention is to provide a heat energized refrigerator comprising three variable volume chambers swept by two displacers in which the motion of the displacers is self-sustained by incorporating the displacers in a spring-mass system in which the displacers each vibrate at resonance frequency in a properly phased relationship to produce the necessary mechanical work for displacer motion.

Another object of my invention is to provide a heat energized refrigerator comprising three variable volume chambers swept by two displacers in which the motion of the displacers is self-sustained by incorporating the displacers in a spring-mass system in which the displacers each vibrate at resonance frequency in a properly phased relationship; the exciting force of the spring-mass system being provided through utilization of the pressure fluctuations of the system to produce the necessary mechanical work for displacer motion.

With these and other objects in view, as will hereinafter more fully appear, and which will be more particularly pointed out in the appended claims, reference is made now to the following description taken in connection with the accompanying drawings in which:

FIGURE 1 is a schematic of a constant volume, variable pressure heat energized refrigerator with which my invention is utilized showing the various positions of the displacers at different stages during its thermodynamic process.

FIGURE 2 is a graph showing the ratio of the instantaneous pressure to the mean system pressure for the above thermodynamic process with the points A, B, C, and D corresponding to the positions of displacers shown in FIGURES 1A, 1B, 1C, and 1D, respectively.

FIGURE 3 is a sectional view of an apparatus for producing refrigeration by having three variable volume chambers swept by two displacers in which the displacers are incorporated into a spring-mass suspension system in accordance with my invention.

FIGURE 4 is a schematic of the spring-mass system of FIGURE 3.

FIGURE 5 is a schematic of an excitation system which utilizes the pressure fluctuation of the thermodynamic process acting on the lower displacer of FIGURE 3 to produce a driving force for the spring-mass system of FIGURES 3 and 4.

FIGURE 6 is a sectional view of an alternate embodiment of a spring-mass suspension system for the displacers in accordance with my invention.

Description of cycle operation More particularly, FIGURES 1A, 1B, 1C, and 1D show a cylinder 12 having a pair of reciprocable displacers 14 and 16 which define three variable volume chambers 13, 20, and 22.

The variable volume chambers 18, 2t and 22. are interconnected through upper and lower regenerative heat exchangers 24 and 2-6, respectively.

Each of the variable volume chambers are shown in a heat exchange relationship with the coils 1'7, 19, and 21, respectively. For simplicity, the coils have been omitted in FIGURES 1B, 1C, and 1D.

The basic principle of cycle operation can be simply stated: heat will flow through a boundary into a space if a part of the gas in the space is allowed to escape. The simplest example of this process is a leaking bottle of pressurized gas. The pressure of the gas in the bottle is naturally decreasing and the temperature would also decrease if the container was insulated. However, if the walls of the container have intimate contact with the gas (small diameter tubes, closely spaced flat panels, etc.), the gas will maintain the same temperature by transferring heat from the wall to the gas. Thus, the gas will absorb heat at constant temperature as the pressure decreases,

This principle is employed below to describe the heat transfer in two of the three variable volume chambers. The converse of this principle, pressurization of a gas at constant volume is used to describe the heat transfer in the third variable volume chamber.

The cylinder 12 shown in FIGURES 1A through 1D is of fixed volume and is sealed to contain a fixed mass of gas. The displacers 14 and 16 are used to displace gas from one variable volume chamber or temperature region of the cylinder 12 to a region at another temperature. For example, suppose the chamber 18 is taken as a hot region having a temperature of 1240 F., the chamber 2th as an intermediate region having a temperature of F., and the chamber 22 as a cold region having a temperature of 40 F. Assuming the displacers 14 and 16 to be in the position shown in FIGURE 1A, the'volume of chamber 20 is then zero with 23% of the fixed mass of gas being in the hot region 18 at a temperature of 1240 F. with the remaining 77% being in the cold region 22 at a temperature of 40 F. In the following analysis, the volume of the gas in the regenerators is assumed to be negligible for simplication. While the additional volume of gas in the regenerator will have some effect on the system in that specific values will be altered, the basic principle of operation will remain the same.

The displacers 14 and 16 in the actual cycle reciprocate with a periodic motion approximating simple harmonic motion. The displacers 14 and 16 are 90 to 120 out of phase for a reason which will be given later. However, to facilitate a clear description of the piston motion and the attendant heat transfer processes, the motion is described here as a three-step process. Linear motion of pistons is assumed and the resulting configurations at the beginning and end of each step are shown in FIG- URES 1A, 1B, 1C, and 1D. A summary of the variation in system pressure is shown in FIGURE 2. The pressure is plotted as the ratio of the instantaneous system pressure to the mean system pressure for the entire cycle, with the points A, B, C, and D on the pressure ratio curve corresponding to the pressure ratio of the system when displacers are positioned as shown in FIGURES 1A, 1B, 1C, and 1D.

The first of the three steps is the refrigeration step. This is accomplished by motion of the displacer 14 from the center to the top position, that is, from the position shown in FIGURE 1A to the position shown in FIG- URE 1B. This motion displaces the gas from the hot region 18 to the intermediate region 20 through the upper regenerator 24. The gas in moving through the regenerator 24 stores heat in the regenerator 24 and is, therefore, cooled. This cooling of a portion of the total mass of the gas reduces the pressure in the system. Since the cold region 22 is maintained at constant volume during this step, the decrease in system pressure will cause 22% of the gas to leavethe chamber 22 and enter the intermediate chamber 20 absorbing heat from the lower regenerator 26 as it passes through it. Like the bottle of escaping gas previously discussed, the cold chamber 22 absorbs heat from its environment (coil 21) to maintain the temperature of the gas remaining in the chamber constant at 40 F. This heating of the portion of gas passing through the lower regenerator 26 increases the system pressure slightly. However, since much more heat is being stored in the upper regenerator (23% going from 1240 F. to 140 F.) than is being released in the lower regenerator (22% going from 40 F. to 140 F.) the net effect is the reduction in system pressure. That is, as the displacer 14 moves from the position of FIGURE 1 to the position of FIGURE 2, the pressure of the system changes from point A to point B in FIGURE 2 causing the flow from chambers 18 and 22 to chamber 20; the reduction of gas in chamber 22 causing heat to be absorbed from coil 21. The coil 21 thus is a refrigeration source.

In the second of the three steps, both the displacers 14 and 16 move down together, that is, from the positions shown in FIGURE IE to the positions shown in FIGURE 1C. The resultant effect on the working fluid is the displacement of gas from the cold region 22. In being displaced, 26% of the gas enters the hot region 18 with the remaining 29% entering the intermediate chamber 20 to increase the amount of gas therein from 45% to 74%. In this step of the process, available heat previously stored in the regenerators 24 and 26 is used to heat the gas passing through them. The result is an increase in system pressure from point B to point C attendant with the heat addition to the displaced gas. The additional gas, 29%, that has entered the intermediate region 20 is the converse of gas escaping from a bottle. In this case, the gas entering the intermediate region 20 must reject heat if its temperature is to be maintained constant. The result is heat rejection from the intermediate region 20. The reject heat is absorbed by coil 19 which in turn dumps the heat to atmospheric (not shown).

FIGURE 1D shows the final step and completion of the cycle where the bottom displacer 16 moves up to the central location as shown in FIGURE 1D.

In this step, gas is displaced from the intermediate chamber 20 to the cold chamber 22 storing heat in the lower regenerator 26 in the process. This reduction in the temperature of the gas results in a reduction of system pressure and a consequent flow of 3% of the hot gas from the hot region or chamber 18 to the cold chamber 22. The hot gas flowing to the cold chamber 22 passes through both regenerators 24 and 26 storing heat therein. The escaping gas from the hot region 18 again is like the bottle of escaping gas and requires heat input to maintain the region 18 temperature constant. This heat input which provides the energizing portion of the cycle is supplied through the upper coil 17.

It should be noted that the third step, 1C to 1D is analogous to the first step 1A to 1B. In both steps, gas escapes from a region of constant volume and heat input is required to maintain a constant temperature.

In the above discussion, the principle of operation was explained on the fact that a constant volume absorbs heat from its environment if some of the gas is allowed to escape. In the actual cycle, the volume is not constant. This fact complicates the explanation but does not effect the outcome.

Actually, as described above, the heat pumping system is a Stirling refrigerator being driven by a Stirling engine. An ideal Stirling refrigerator operating between 40 F. and F. has a ratio of heat absorption to work input of 5 while an ideal Stirling engine operating between 1240 F. and 140 F has a ratio of work output to heat input of 0.65. Thus using the work output of the engine as input to the refrigerator results in a ratio of 3.2. Thus, appropriate motion of two displacers 14 and 16 and the resultant displacement of gas from three regions 18, 20, and 22 results in refrigeration at the cold region 22, heat rejection at the intermediate region 20 and heat input at the hot region 18, with the ratio of refrigeration to heat input being 3.2.

The entire three step process is summarized in FIGURE 1 with the variation in system pressure being shown in FIGURE 2. In addition to its use in promoting heat transfer, the variation in system pressure is employed to power the displacer motion. This latter function of the system pressure variation is described below.

Displacer suspension Referring to FIGURE 3, the cylinder 12 is shown with the reciprocable displacers 14 and 16 interconnected with a spring system. The interconnecting passages and regenerators 24 and 26 between the variable volume chambers 18, 20, and 22 have been omitted for simplicity. More specifically, the cylinder 12 is shown as having a central stud 28 extending from its bottom end wall 30. The stud 28 comprises a lower rod portion 34 and an enlarged hollow upper portion 32. The lower displacer 16 is hollow with its upper and lower faces 36 and 38 slidably mounted on the enlarged hollow upper portion 32 and lower rod portion 34, respectively, of the central stud 28. The fit between faces and the stud 28 is sufficiently close so that a substantially fluid tight compartment 37 is formed by the inner walls of displacer 16 and the stud 28 while allowing relative motion between the parts.

The enlarged hollow upper portion 32 has an outwardly projecting central flange 40. A coil spring 42 encircles the enlarged hollow upper portion 32 between the flange 40 and the upper displacer face 36. The spring 42 is secured to both the flange 40 and the upper face 36 so as to be bidirectional, that is, the spring 42 acts in both tension and compression. The upper displacer 14 has a central stem 44 with a disc 46 at its lower end. The disc 46 is reciprocable within the hollow cylindrical upper portion 32 of the central stud 28. A second coil spring 48 is secured at one end to the disc 46 and at the opposite end to an internal shoulder 50 in the enlarged hollow upper portion 32. Thus both displacers 14 and 16 are connected by bidirectional springs to the stud 28 which in turn is fixed to and part of cylinder 12.

A number of stems 52 extend upward from the bottom face 38 of the lower displacer 16 into the hollow upper portion 32 of stud 28. The stems 52 mount a second disc 54 which is also reciprocable with the hollow cylindrical upper portion 32. A third bidirectional spring 56 is secured to the discs 46 and 54 and resiliently connects the displacers 14 and 16.

The disc 46 has a number of air holes 47 and the second disc 54 is shown with an air hole 55. This provides for the flow of air through the discs as they reciprocate with the hollow upper portion 32 of the stud 28 so that no portion of the hollow stud will act as a damping chamber.

Displacer motion As mentioned above, the displacers 14 and 16 reciprocate with periodic motion with a phase difference of from 90 to 120. Each displacer is connected to the cylinder by a spring and a third spring is employed to directly couple the two displacers. The periodic motion of the two displacers is provided by the above spring-mass vibration system which utilizes the system pressure variation as a driving force.

Stated another way, the thermodynamic requirements dictate certain displacer motions. This in turn produces a certain system pressure variation. By resiliently suspending the displacers and making one of the displacers a differential piston to create a driving force, a forced vibratory spring mass system is created. If at resonance, the periodic vibratory motion of the displacers coincides with the thermodynamic motion required, the system becomes self-sustained, that is, no external mechanical work is required to drive the displacers. The only source of energy for the system is the heat input to the hot region 118. The following discussion is directed to collaborating the required thermodynamic and vibratory displacer motions.

A simple schematic of the system is shown in FIGURE 4 in which the displacers 14 and 116 are represented by masses M and M respectively, with the springs 42, 48, and 56 shown as having spring constants K K and K respectively. This schematic represents a damped twodegree of freedom forced vibratory spring-mass systems which will operate at resonance after initially having been set in motion. There are, however, two requirements for stable operation of this system: damping must be added to the cycle in an amount equal to that dissipated by the damping. The damping is represented by the dashpots 58 and 60 for the displacers l4 and 16, respectively.

The actual damping of the system is comprised of two parts. The first component is Coulomb, or friction damping. It is of essentially constant magnitude and its direction of application is always opposed to the direction of velocity. The second type of damping results from the aerodynamic flow losses of the working fluid flowing through the system. This second type of damping is the greatest part of the damping force and can be used to represent the total damping in a preliminary analysis. It is proportional to the second power of velocity and can be represented by an equation of the form where P is the damping force, C is the damping constant, X is the displacer velocity, and the subscripts 1 and 2 represent the displacers 14 and 16, respectively. The equations of motion for each displacer then may be expressed as v where X and X are the displacer displacements and accelerations, respectively. The subscripts and other symbols have been explained above.

As previously mentioned, energy must be added to the system to compensate for that dissipated by damping. The next step is to compute the excitation or driving force F necessary to keep the system in motion. This driving force F may be produced by the energy addition system shown in FIGURE 5. This simple energy addition system is comprised of the stationary stud 28 having an enlarged upper portion 32 about which the top surface of the cold displacer 16 reciprocates. The enlarged upper portion 32 thus creates a larger surface area on the lower face 38 of the cold displacer 16 than that on the top face 36 of the cold or lower displacer 16. Because the pressure drop through the heat exchangers and regenerators is small compared to pressure in the system at any time, the instantaneous pressure on the bottom face is essentially equal to the pressure on the top face. The compartment 37 inside of the hollow cold displacer 16 is maintained at the system mean pressure because of the sealing engagement of the displacer faces with the stud. The effect of the volume change of chamber 37 because of the various length of penetration of hollow upper portion 32 of the central stud 28 is assumed negligible.

Thus the force F can be expressed as a function of the instantaneous and mean pressures:

where A is the cross sectional area of the cylinder, A is the area of the displacer top 36, p is the instantaneous pressure and P is the mean system pressure. Note that the area of the rod piston 34 has been assumed negligible and the area of lower face 38 has been equated to the cylinder cross sectional area A. For convenience, let the cross sectional area of the cylinder equal 1.0 and substitute the stud surface area, A for the differential area of the lower displacer. Equation 4 then becomes:

Note from Equation 5 that a positive or upward force is produced whenever the instantaneous pressure p is greater than the mean pressure P The instantaneous pressure in turn is a function of the volume of the chambers 18, 20, and 22, the temperature of the gas therein and the total mass of the gas. Thus, there is a relationship between the displacer motion required for the vibratory system and that required for the thermodynamic cycle. Since a fixed mass of gas is used in the system, the following equation can be written. As before, the gas in the interconnecting passageways and regenerators and its effects are considered negligible for simplicity.

where Mg is the total mass of the gas and the subscripts represent the mass of gas in the respective chambers 18, 20, and 22. From the gas law, we know that The volumes of the chambers 18, 20, and 22 are related to the displacement X and X of the displacers 14 and 16 as can .be seen from FIGURES 3 and 4. Considering the area of the stems 34 and 44 negligible and recalling that the cylinder cross sectional area was chosen as 1.0 for convenience the relationship may be derived.

and the instantaneous pressure expressed as:

Equation 14 relates the instantantaneous pressure to the positions X and X of the displacers 14 and 16, respectively. The relationship having been shown, solution to the problem is a mere matter of computation.

Since the driving force F is a function of the instantaneous pressure, it is also a function of the displacer positions X and X In any harmonic or periodic system where energy is transferred between an exciting force and a damped member, the exciting force must lead the motion. This adds an additional requirement of properly phasing the motion of the displacers 14 and 16. As previously stated, the displacers are from 90 to 120 out of phase so that a driving force can be created which will lead the required motion for the bottom displacer 16. Return to FIGURES 1 and 2 and recall from Equation 5 that a positive or upward driving force F is produced whenever the instantaneous pressure p is greater than the mean system pressure or expressed another way whenever the ratio of the instantaneous to mean pressure ratio is greater than 1.0. The bottom displacer 16 moves upwardly from FIGURE to FIGURE 1D. The instantaneous pressure, however, becomes greater than mean pressure between points B and C prior to the upward movement of the displacer 16. Thus the system pressure will produce an upward increasing driving force preceding the requirement for the upward movement of displacer 16.

We now have the system operating so that a driving force F is created to move the bottom displacer 16 with the required motion. The displacer top 14 in turn is moved by the forces created in the spring system by the moving bottom displacer 16. Referring to FIGURES 3 and 4, as the bottom displacer 16 is moved upwardly by the force F, spring 42 is stretched while spring 56 is compressed. Compression of spring 56 will create an upward force acting on the top displacer 14. Relating this back to FIGURES l and 2 between B and C, the instantaneous pressure creates an upward increasing force F on the bottom displacer 16. The bottom displacer 16 subsequently moves upward from C to D from the position shown in FIGURE 1C to that of FIGURE 1D. This movement compresses spring 56 creating an upward force acting on the upper displacer 14. As before, the force leads the motion and the upper displacer 14 subsequently moves upwardly from FIGURE 1A to FIGURE 1B. (Note FIGURE 1D and 1A are identical.) The upward movement of the upper displacer 14 also causes a storage of energy in spring 48.

Meanwhile stretching of spring 42 creates a downward force which opposes the upward driving force F acting on the bottom displacer 16. The pressure ratio, however, continues to be greater than one until at one point between A and B, the'instantaneous pressure drops below mean pressure. Now energy in the stretched spring 42 aids the downward driving force and the lower displacer 16 is subsequently moved downwardly during the B to C interval.

With the downward movement of the lower displacer 16, the compression on spring 56 is released. The energy previously stored in spring 48 then creates a downward force which leads the required subsequent downward movement of the upper displacer 14. Relating this to FIGURE 1 and 2, we see a pressure ratio below 1.0 preceding point B. This corresponds to a downward exciting force F acting on the lower displacer 16. The lower displacer 16 then moves downwardly from FIGURE 1B to FIGURE 1C. In moving downwardly, the compression on spring 56 is released and the upper displacer 14 is also moved downwardly under the influence of the energy stored in spring 48. While the heat rejection step was previously described as the simultaneous downward movement of both displacers, in actuality, the downward movement of the bottom displacer 16 precedes that of the upper displacer 14 since they are out of phase. In addition to being out of phase in their actual movement, the motion of the displacers is periodic and approximates harmonic motion though not precisely harmonic. The system, however, is resonant.

In summary, the proper phasing of the displacers 14 and 16 together with the proper selection of spring rates and displacer masses produces a heat refrigeration system in which the motion of the displacers is sustained. In other words, the forces created by the differential pistons and springs will cause the displacers to move with the required motion in a resonant condition once the system has been initiated. To start the apparatus in motion, any means may be utilized. An example would be a solenoid starter where a coil 60 is energized to attract an armature 62 which in turn causes a non-magnetic plunger 64 to push the upper displacer 14 downwardly. Such a starter would require only one energization of the coil 60 and a single stroke to initiate system motion. From this initial movement, the system would rapidly build up to a resonant condition.

FIGURE 6 arrangement While preferably, the spring 42, 48, and 56 should be in identical environments as in the FIGURE 4 apparatus, this is not absolutely essential. In FIGURE 6, an alternate arrangement is shown wherein this does not occur. Here the cylinder 112 has upper and lower displacers 114 and 116, respectively. The lower displacer 116 is mounted on a central stud 128 and has differential area faces. A coil spring 142 embraces the upper portion 132 of stud 128 and is secured to a flange 140 thereon and to the lower displacer 116. The difference in this embodiment lines in the location of the remaining springs 148 and 156. Both lie in chamber with the spring 148 connected between stud 128 and displacer 114 while spring 156 is connected between both displacers. This configuration will operate in the same manner; however, the springs are not in identical environments.

Thus, it can be seen that this invention provides a heat energized refrigerator comprising three variable volume chambers swept by two displacers in which the motion of the displacers is self-sustaining, that is, the heat energized refrigerator requires no external power source to drive the diplacers. It should be understood, of course, that the foregoing disclosure relates to only preferred embodiments of the invention and that numerous modifications or alterations may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

I claim:

1. In a heat energized refrigerator or the like having a pair of displacers reciprocable within a cylinder to provide three variable volume chambers which are interconnected through regenerative heat exchangers to become progressively cooler regions when heat is added to one of the chambers and a constant volume of fluid flows between the variable volume chambers through the regenerators at varying pressures, the improvement comprising:

a fixed central stud extending into the cylinder, said stud having an enlarged hollow upper portion,

a first hollow displacer having a pair of spaced faces slidably mounted on said stud, one of said faces movably engaging said upper portion, said one face being of smaller area than said other face,

a stem on said first displacer slidably mounted in said hollow upper portion,

a compartment defined by said hollow differential displacer and stud,

means to maintain the pressure in said compartment substantially at the mean pressure of the system,

a first spring disposed within said compartment and secured to said first displacer and said stud,

a second displacer having a second stem slidably mounted in the hollow upper portion of said stud,

a second spring disposed in said hollow portion and secured to said second stem and said hollow portion, and

a third spring disposed in said hollow portion and secured to said first and second stems, whereby the displacers and springs become a spring-mass system reciprocating at a resonance frequency with the force created by fluid pressure acting on the differential area faces on said first displacer sustaining the system motion.

2. In a heat energized refrigerator or the like having a pair of displacers reciprocable within a cylinder to provide three variable volume chambers which are interconnected through regenerative heat exchangers to become progressively cooler regions when heat is added to one of the chambers and a constant volume of fluid flows between the variable volume chambers through the regenerators at varying pressures, the improvement comprising:

a fixed central stud extending into the cylinder, said stud having an enlarged hollow upper portion,

a first hollow displacer having a pair of spaced faces slidably mounted on said stud, one of said faces sealingly, movably engaging said upper portion, said one face being of smaller area than said other face,

a stem on said first displacer slidably mounted in said hollow upper portion,

a compartment defined by said hollow differential displacer and said stud,

a first spring disposed within said compartment and secured to said first displacer and said stud,

a second displacer having a second stem slidably mounted in the hollow upper portion of said stud,

a second spring disposed in said hollow portion and secured to said second stem and said hollow portion, and

a third spring disposed in said hollow portion and secured to said first and second stems, whereby the displacers and springs become a spring-mass system reciprocating at a resonance frequency with the force created by fluid pressure acting on the differential faces on said first displacer sustaining the system motion.

3. In a heat energized refrigerator or the like having a pair of displacers reciprocable within a cylinder to provide three variable volume chambers which are interconnected through regenerative heat exchangers to become progressively cooler regions when heat is added to one of the chambers and a constant volume of fluid flows between the variable volume chambers through the regenerators at varying pressures, the improvement comprising:

a fixed central stud extending into the cylinder, said stud having an enlarged upper portion,

a first hollow displacer having a pair of spaced faces slidably mounted on said stud, one of said faces movably engaging said upper portion, said one face being of smaller area than said other face,

a compartment defined by said hollow differential displacer and said stud, means to maintain the pressure in said compartment substantially at the mean pressure of the fluid,

a first spring disposed within said compartment and secured to said first displacer and said stud,

a second displace-r axially spaced from said first displacer,

a second spring secured to said second displacer and said hollow portion, and

a third spring secured to said first and second displacers,

whereby the displacers and springs become a springmass system reciprocating at a resonance frequency with the force created by fluid pressure acting on the differential area faces on said first displacer sustaining the system motion.

4. In a heat energized refrigerator or the like having a pair of displacers reciprocable within a cylinder to provide three variable volume chambers which are inter connected through regenerative heat exchangers to become progressively cooler regions when heat is added to one of the chambers and a constant volume of fluid flows between the variable volume chambers through the regenerators at varying pressures,the improvement comprising:

a fixed central stud extending into the cylinder, said stud having an enlarged upper portion,

a first hollow displacer having a pair of spaced faces slidably mounted on said stud, one of said faces sealingly movably engaging said upper portion, said one face being of smaller area than said other face,

a compartment defined by said hollow differential displacer and stud,

a first spring disposed within said compartment and secured to said first displacer and said stud,

a second displacer axially spaced from said first displacer,

a second spring secured to said second displacer and said hollow portion, and

a third spring secured to said first and second displacers, whereby the displacers and springs become a spring-mass system reciprocating at a reconance frequency with the force created by fluid pressure acting on the differential area faces on said first displacer sustaining the system motion.

5. In a heat energized refrigerator or the like having a pair of displacers reciprocable within a cylinder to provide three variable volume chambers which are interconnected through regenerative heat exchangers to become progressively cooler regions when heat is added to one of the chambers and a constant volume of fluid flows between the variable volume chambers through the regenerators at varying pressures, the improvement comprismg:

a fixed central stud extending into the cylinder,

a first displacer having a pair of spaced faces of different area slidably mounted on said stud,

a first spring secured to said first displacer and said stud,

a second displacer axially spaced from said first displacer,

a second spring secured to said second displacer and said stud, and

a third spring secured to said first and second displacers whereby the displacers and springs become a springmass system recirprocating at a resonance frequency with the force created by fluid pressure acting on the ditferential area faces on said first displacer sustaining the system motion.

6. in a heat energized refrigerator or the like having a pair of displacers reciprocable within a cylinder to provide three variable volume chambers which are interconnected through regenerative heat exchangers to become progressively cooler regions when heat is added to one of the chambers and a constant volume of fluid flows between the variable volume chambers through the regenerators at varying pressures, the improvement comprising:

a first hollow displacer having a pair of spaced faces of different area slidably mounted in said cylinder,

a first spring disposed within said cylinder and secured to said displacer and said cylinder,

a second displacer slidably mounted in said cylinder,

11 a second spring disposed in said cylinder and secured to said second displacer and said cylinder, and a third spring secured to said first and second displacers whereby the displacers and springs become a springrnass system reciprocating at a resonance frequency with the force created by fluid pressure acting on the differential area faces on said first displacer sustaining the system motion. 7. In a heat energized refrigerator or the like having a pair of displacers reciprocable within a cylinder to provide three variable volume chambers which are interconnected through regenerative heat exchangers to become progressively cooler regions when heat is added to one of the chambers and a constant volume of fluid flows between the variable volume chambers through the regenerators at varying pressures, the improvement comprising:

a first hollow displacer having a pair of spaced faces of different area slidably mounted in said cylinder, a second displacer slidably mounted in said cylinder, a first spring disposed in said cylinder and secured to said second displacer and said cylinder, and a second spring disposed in said hollow portion and secured to said first and second displacers, whereby the displacers and springs become a spring-mass system reciprocating at a resonance frequency with the force created by fluid pressure acting on the differential area faces on said first displacer sustaining the system motion.

8. In a heat energized refrigerator on the like having a pair of displacers reciprocable within a cylinder to provide three variable volume chambers which are interconnected through regenerative heat exchangers to become progressively cooler regions when heat is added to one of the chambers and a constant volume of fluid flows between the variable volume chambers through the regenerators at varying pressures, the improvement comprising:

first resilient means secured to one of said displacers and said cylinder, second resilient means secured to the other of said displacers and said cylinder, third resilient means coupling said displacers and cyclic excitation force means acting on one of said displacers whereby the displacers and springs become a force spring-mass vibrational system with said displacers reciprocating at a resonance frequency to sustain the required thermodynamic system motion.

References Cited by the Examiner UNITED STATES PATENTS 1,275,507 8/ 1918 Vuilleumier 626 2,045,152 6/1936 Iebre 626 2,127,286 8/1938 Bush 626 2,157,229 5/1939 Bush 626 2,567,454 9/1951 Taconis 626 30 WILLIAM J. WYE, Primary Examiner. 

1. IN A HEAT ENERGIZED REFRIGERATOR OR THE LIKE HAVING A PAIR OF DISPLACERS RECIPROCABLE WITHIN A CYLINDER TO PROVIDE THREE VARIABLE VOLUME CHAMBERS WHICH ARE INTERCONNECTED THROUGH REGENERATIVE HEAT EXCHANGERS TO BECOME PROGRESSIVELY COOLER REGIONS WHEN HEAT IS ADDED TO ONE OF THE CHAMBERS AND A CONSTANT VOLUME OF FLUID FLOWS BETWEEN THE VARIABLE VOLUME CHAMBERS THROUGH THE REGENERATORS AT VARYING PRESSURES, THE IMPROVEMENT COMPRISING: A FIXED CENTRAL STUD EXTENDING INTO THE CYLINDER, SAID STUD HAVING AN ENLARGED HOLLOW UPPER PORTION, A FIRST HOLLOW DISPLACER HAVING A PAIR OF SPACED FACES SLIDABLY MOUNTED ON SAID STUD, ONE OF SAID FACES MOVABLY ENGAGING SAID UPPER PORTION, SAID ONE FACE BEING OF SMALLER AREA THAN SAID OTHER FACE, A STEM ON SAID FIRST DISPLACER SLIDABLY MOUNTED IN SAID HOLLOW UPPER PORTION, A COMPARTMENT DEFINED BY SAID HOLLOW DIFFERENTIAL DISPLACER AND STUD, MEANS TO MAINTAIN THE PRESSURE IN SAID COMPARTMENT SUBSTANTIALLY AT THE MEAN PRESSURE OF THE SYSTEM, 